104222-90-4Relevant academic research and scientific papers
Thermolysis and photolysis of a γ-azoperester. Cyclization of γ-azo and γ-perester radicals
Engel, Paul S.,He, Lin Shu,Smith, William B.
, p. 6059 - 6065 (1997)
Thermolysis of azoperester 5 affords γ-azo radical 14, which cyclizes to hydrazyl radical 15 at a rate of 1.3 x 106 M-1s-1 at 11°C. Our experimental results are consistent with loss of a methyl radical from 15 to afford 2-pyrazoline 9, which is oxidized in situ by the starting S to pyrazole 6. This unusual and endothermic β-scission can be rationalized if the odd electron 9n 15 is better aligned with the CH3-C bond than with the weaker t-Bu-N bond. The fact that 5-endo cyclization of 14 in 5 x 107 faster than that of the analogous olefinic radical 30 led us to carry out ab initio calculation on simplified structures. ΔH((+)) for methyl radical addition to diimide is only 0.84 local/mol lower than for addition to ethylene and the exothermicity is only 3.5 kcal/mol greater. However, the smaller C-N=N than C-C=C bond angle leads to a ΔH((+)) 13.3 cal/lower for 5-endo cylclization of 4,5-diazapenten-1-yl than for the analogous 4-penteryl radical. Photolysis of 5 selectively cleaves for azo group, producing γ-perester radical 20. This species undergoes intramolecular attack on the peroxide linkage to form lactone 23 at a rate of 1.5 x 104 s-1 at 22°C. The cyclization rate of 20 is slow enough that 5 could be used as a photochemical bifunctional initiator, but cyclization of 14 to the azo group is so rapid that this radical would only rarely attack a monomer, initiator, but cyclization of 14 to the azo group is so rapid that this radical would only rarely attack a monomer.
